1. Field
The following description relates to a method of fabricating yttrium aluminum garnet (YAG) phosphor particles and synthesis method thereof, and to a spherical hollow YAG phosphor, spherical hollow YAG phosphor particles, and synthesis method thereof.
2. Description of Related Art
There are two major methods of obtaining white color emission using light emitting diodes (LEDs). One method involves combining light from a red LED, a green LED, and a blue LED. The other method involves applying a yellow phosphor to light emitted from a blue LED. In recent years, the application of white LED for lighting has substantially increased, and the latter method of using a yellow phosphor with a blue LED is widely used to obtain white light from LEDs. In this method, obtaining yellow phosphor with high efficiency in addition to obtaining high performance from the blue LED has become an important technical challenge.
A white LED light emitting element is generally formed in such a manner that a yellow phosphor is coated on a blue LED chip. The phosphor roughly includes a parent body and an activator element. The yellow phosphor that is widely used may use Ce as an activator in Y3Al5O12 (YAG; Yttrium Aluminum Garnet) having a garnet structure. A YAG phosphor with Ce added thereto may generate intense excitation of light in a blue area of the spectrum and absorb the generated light to have a wide greenish yellow color. Therefore, the YAG phosphor may harmonize with the blue LED chip. In addition, a phosphor including YAG as a parent body is physically and chemically very stable due to its structural characteristics.
A conventional YAG phosphor is generally obtained by mixing, drying, calcining, and grinding metal oxides using a solid-state reaction method. Because this process is a time-consuming process and uses oxides as starting materials, the metal oxides should be calcined at a temperature of 1,600° C. or higher. As a result, several intermediate products such as Y4Al2O9 (YAM) and YAlO3 (YAP) may easily get mixed in the composition of the final product due to insufficient mixing and low reactivity of raw materials.
In addition, the composition and particle sizes of the final product are not uniform due to a solid-state reaction between particles and a long-time grinding that is required. Therefore, purity degradation and florescent characteristic degradation may occur due to pollution of the product. For example, when fabricating YAG:Ce phosphor powder, a yttrium oxide, an aluminum oxide, a cerium oxide, and the like are mixed for a long time to obtain a uniform mixture. The mixture is dried and calcined at a temperature of 1,700° C. or higher. In addition, even though a flux such as BaF2 is added, a heat treatment temperature should be 1500° C. or higher. The strongly cohesive powder has to be grounded again for a long time. Thus, impurities may get mixed into the powder, and the particle size of the resulting powder is not uniform. The particle size of a phosphor powder generally needs to be 3 μm or less, as well as be uniform in size with a substantially spherical shape, to achieve high efficiency. However, a phosphor powder obtained by the solid-state reaction method does not have uniform particle sizes. For example, in a general distribution, when the average particle size is about 5 μm, a wide distribution range of typically about 1 to 20 μm may result.
The conventional commercial YAG phosphor has a low packing density due to the non-uniform shapes and sizes. Therefore, the luminance of the YAG phosphor may deteriorate, and a light-scattering loss may occur when the YAG phosphor is used in an LED chip.